What Should I Do About A Persistent Golf Ball-sized Knot On My Lower Right Arm That Appeared After I Hit It Last Saturday Night?

I hit my lower right arm Saturday night last week and a few days ago and that sunday morning i had a golf ball size knot on my arm and redness on the inside of my arm a few days later. I still have the knot on my arm but the color around it went away and it doesn t hurt at all but still there and doesn t move. I used which hazel, ice and muscle cream but I won t go down. What should i do?